Power regulator



Dec. 6, 1960 Filed July 1, 1957 D.C. CONTROL A. NUUT EIAL 2,963,638

POWER REGULATOR 2 Sheets-Sheet 1 LOAD -5 PNP FIG. 4

August Nuut Murray J Hillman INVENTORS ATTORNEY V Dec. 6, 1960 A. NUUTETAL 2,963,633

POWER REGULATOR Filed July 1, 1957 2 Sheets-Sheet 2 MAX. LIMlT SET BYA.C. SUPPLY MINIMUM VALUE MAGNETiZING CURRENT (EXAGGERATED) Augusf NuufMurray J. Hillman INVENTORS ATTORNEY United States Patent POWERREGULATOR August Nuut, Glendale, and Murray J. Hillman, West Covina,CaliL, assignors to Hycon Mfg. Company, Pasadena, Calif., a corporationof Delaware Filed July 1, 1957, Ser. No. 668,964

10 Claims. (Cl. 323-22) Our invention relates generally to powerregulators and more particularly to a transistor power regulatorincorporating a saturable core reactor for control of power delivered toa load.

It is an object of our invention to provide means including a powertransistor and a saturable core reactor for effegting proportionalcontrol of power delivered to a Another object of the invention is toprovide an extremely simple circuit having high efficiency of control ofdelivered power.

Another object is to provide a transistor power regulator which can becontrolled either by an alternating current or direct current controlsignal.

A further object of our invention is to provide a transistor powerregulator having a large dynamic control range of output power. g

Briefly, and considered in general terms, the foregoing objects arepreferably accomplished by providing a saturable core reactor having aprimary and a secondary winding which are supplied by respectivein-phase alternating voltages, the primary winding circuit including acontrol transistor and a diode-connected transistor, and the sec-.

ondary winding circuitincluding a crystal diode and a power transistorsupplying a load. Another crystaldiode 1s connected to provide a supplyvoltage to the collector of the power transistor, and a suitable inputnetwork is provided to apply a control signal to the control transistor.Application of the control signal to the control transistor produces areset voltage in-theprimary winding which resets the saturable corereactor each cycle inversely according to the magnitude of the controlsignal applied. The subsequent pulse output from the saturable corereactor is variable in pulse width according to the magnitude of theapplied control signal, and is applied to the power transistor tocontrol the power delivered to the load.

Our invention possesses other objects and advantage ous features, someof which, together with the foregoing, will be rendered apparent by thefollowing detailed description of a preferred embodiment of ourinvention to be read in conjunction with the attached drawings, inwhich:

Figure 1 a circuit diagram of a preferred embodiment of our invention;

Figure 2 is a fragmentary drawing of a section of the circuit of Figure1 illustrating the load connected in the collector circuit of the powertransistor;

Figure 3 is a fragmentary drawing of another section of the circuit ofFigure 1 showing acircuit arrangement for direct current control;

Figure 4 is a fragmentary drawing of yet another sec: tion of thecircuit of Figure 1 illustrating the connection of acrystal diode inplace of a diode-connected transistor;

Figure 5 is a graph showing a plot for the circuit of Figure 1 of loadvoltage versus control voltage and the effects of variations ofdifferent circuit operating conditions'; and V Figure 6 is a series ofgraphs showing curves plotted ice to the same abscissa time scale andwhich illustrate the relationship between different voltages andcurrents in the circuit of Figure l.

A preferred embodiment of our invention is shown in Figure l. A 30 volt,400 c.p.s. supply voltage e for example, is applied acrossautotransformer 1 through terminals 2 and 3 which are connected torespective ends 1a and 1b of autotransformer 1. Terminal 3 (and end 1b)is grounded as illustrated. A 3 volt tap 10, for example, providing avoltage e is connected to one end of primary winding N1 of a saturablecore reactor T1, the other end of primary winding N1 being connected tothe emitter of control transistor XR-l. The base of transistor XR-l iscoupled to a control signal terminal 4 through a capacitor C, and thecollector of transistor XR-1 is connected directly to the emitter ofdiode-connected transistor XR-2 which has its base and collector tiedtogether and connected to ground. An input resistor R is connected onone end to the common junction of capacitor C and the base of transistorXR-l, and on the other end to control signal terminal 5, which isconnected to ground. A control signal e of 03 volts, 400 c.p.s., forexample, and in phase with e and 9 can be applied between the terminals4 and 5.

The end 1a of the autotransforrner 1 is connected to one end ofsecondary winding N2 of the saturable core reactor T1 and also to thecathode of a diode CR-l, the anode of which is connected to thecollector of power transistor XR-3. The base of power transistor XR-S isconnected to the anode of diode CR-Z, the cathode of which is connectedto the other end of secondary winding N2. The emitter of powertransistor XR-3 is connected to ground through load L. The turns ratiobetween primary winding N1 and secondary winding N2 is l to 10, forexample, the same as the ratio of e to e such that saturable corereactor T1 is insensitive to fluctuations in line voltage.

Although the load L is shown connected in the emitter circuit of powertransistor XR-S in Figure l, the load L can just as Well be located inthe collector circuit. As indicated in Figure 2, the load L is connectedbetween end 1a of autotransformer 1 (not shown here) and the cathode ofdiode CR-l.

The resistor R-capacitor C input network of Figure 1 can be replaced byany of the usual coupling circuits such as transformer or reactorcoupling. A direct current control is also effective and can be obtainedby deleting resistor R and capacitor C, and connecting a direct currentsource directly between the base of control transistor XR-l and ground.This is illustrated in Figure 3, wherein a positive direct controlvoltage is applied to the base of transistor XR-l. The adjustable tap ofa potentiometer, for example, can be connected to the base of controltransistor XR-l and one end of the potentiometer to ground for asuitable direct current source.

The diode-connected transistor XR-2 connecting with the collector ofXR-1 can, of course, be replaced by a crystal or other suitable typediode CR-3 as shown in Figure 4. Functionally, XR-2 or CR-3 preventsforward conduction through the base to collector junction of transistorXR-l, but the crystal diode CR-3 does not have as low a forwardimpedance as a diode-connected transistor XR-Z. The function of controltransistor XR-1 is to provide power gain with a voltage gain ofapproximately unity.

Operation of the circuit of Figure 1 can best be described withreference to Figures 5 and 6. The waveform of e, is shown as a sine wavein the top graph of Figure 6, and comprises positive half cycles A andnegative half cycles B. The supply voltage e can, however, have anyother waveform, such as a square wave, for example, so long as themaximum amplitude reached is sutficient to just cause saturation ofsaturable core reactor T1 during the negative half cycle B, after fullreset. The voltage e is also a sine wave if e is a sine wave, but is ofa much smaller. amplitude, as indicated in the top graph of Figure 6,because, of the autotransformer connection at 10.

When control signal e which can be a sine wave in phasewith e and isapplied between terminals 4 and 5, the positive half cycleof 2 appearson the emitter of transistor XR-J with substantially no drop inmagnitude andis directed to the lower end of primary winding N1 tooppose the in-phase voltage e applied to the other end of primary,winding N1 fromtap 1c. Depend, ing-upon the magnitude of c which can bevaried as desired; the difference in magnitude between 2 and e appearsas a resetvoltage across primary winding N1. The-magnitude of thisdifference. voltage establishes the output pulse Width supplied to .theload, L. Diodes.

CR-l and CIR-2 respectively prevent application of the positive halfcycle A of:e to the collector and base of power transistor XR3. Withoutdiode CR 2, leakage through the base of emitter junction of powertransistor XR-3 during the positive. vhalfcycle A would tend to resetsaturable core reactor T 1,.which would limit the maximum pulsewidthfrom secondary winding NZ to the base ofpower .transistorXR-S- andconsequently limiting the useful power from the power transistor XR-3.

If e is O, for example, a maximum reset voltage difference equal to eresets saturable core reactor T1 to produce a minimum width pulse outputduring the negative half cycle B. If e is 3 volts or equal to e nodifference voltage is available for reset purposes, and a maximum widthpulse output is obtained in the following negative half cycle. Asubstantially constant reset current i of approximately one milliampere,for example,

flows in primary winding N1 during the positive half cycle A. This isillustrated by the curve in the second graph from the bottom of Figure6.

During the negative half cycle B, a negative half cycle of a is appliedto the base of control transistor XR-I. At the same time, however, anegative half cycle of inphase voltage e appears at the emitter of XR-lthrough primary winding N1. Normally, a negative emitter transistor iseffectively reverse-biased, however, the emitterwand collector-of atransistor can be functionally interchanged such that transistor XR-lwouldconduct but for the inclusion of diode-connected transistor XR-Z.

Diode-connected transistor XR-2 has a very lowfor Or-. dinary crystaldiodes cannot match this requirement, The voltage waveform e from theemitter of controltransistor XR1 to ground is shown by the curve, inthe.

bottom graph of Figure 6.

During the negative half cycle of e the large negative half cycle of eis also applied to the base of power.

transistor XR-3 through secondary winding N2 and diode CR-2. A smallmagnetizing current of about 100 microamperes initially flows insecondary winding N2 T1 occurs.

current i of the power transistor increases suddenly as saturable corereactor T1 saturates, as indicated by the.

sharp drop following the exaggerated magnetizing current portion. Thevoltage 2;, waveform across load I.

generally follows that of the base current of power,

transistor XR-3, as illustrated by the curve in the middle graph ofFigure 6, which is for a resistiveload;

The time or the quickness that saturable core reactor T1 saturatesduring the negative half cycle B is dependent upon the previous resetvoltage magnitude applied duningthepositive half cycle A and which is,inturn, .de-;

pendent upon the applied magnitude of-thein-phase control signal e Thewider the output pulse, the greater will be the power delivered to theload. The ratio or proportion of on-to-ofr' time of the power transistorserves to effect proportional control of power delivered to the loadaccording to the magnitude of a small control signal e Thus, anadjustable magnitude control signal is used to regulate the outputpulsewidth of periodic pulses, and hence the power delivered to a load.

A plot of load voltage e versus the control signale is shown in Figure5. The eflect'of excessive magnetizing current in secondary winding, N2.011. the minimum value of load .voltage e is to raise the minimum levelas indicated by the broken line 6. Excessive impedance in the controlcircuit, such as,would:.be introduced by substitution of a highimpedance crystal diode for diodeconnected transistor XR-2, will alsocause this effect since insufiicient reset voltage is applied acrossprimary winding N1. However, if primary winding N1 had many turns,like:the secondary winding N2 which is designed for a high supplyvoltage, leakage current throughcontroltransistor XR-l would tend toover reset. the saturable core reactor T1 and restrict the maximumoutput to a value less than the maximum limit value imposed,

by the alternating supply voltage. This effect of nudesired reset duringthe positive half cycle A on the maximum output limit is, for example,indicated by the-broken line 7 in Figure 5.

In order to obtain a maximum ratio between the maximum and minimum pulsewidths derivable from the output of saturable core reactor T1, thesaturable core reactor T1 must have the following characteristics toprevent the magnetizing current from prematurely turning on powertransistor XR3 each cycle.

1) The core material for saturablecore reactor T1 must yield thenarrowest possible hysteresis loop to keep the .magnetizing current frommaking unduly large excursions in a cycle.

(2) The core itself must be as small as possible consistent with thedriving power requirements of the power transistor XR-3. Thiseffectively reduces thereluctance of the magnetic path to a minimum andthe required magnetizing current can be kept low.

(3) For a given size core, the highest practicable supply voltage e isrequired. This necessitates the use of a maximum number of turns for thesecondary winding N2 and therefore further reduces the magnetizingcurrent flowing during the portion of the negative half cycle B beforethe saturable core reactor T1 saturates. On the other hand, the primarywinding N1 should have the smallest number of turns for low impedanceconsistent with the minimum voltage drops across control transistor XR-pl and diode-connected transistor XR-3.

Control effected by a direct voltage applied to thebase of controltransistor XR-1 as shown in Figure 3 is similar in operation to controlby an alternating current control signal which is in phase with thesupplyvoltages e and e During the positive half cycle A, a resetvoltage-is produced across primary winding N1 which is dependent uponthe magnitude of the positive direct current control signal applied tothe base of control transistor XR-l, as with alternating currentcontrol. During thenegative half, cycle B, the emitter of controltransistor XR-l is negatively biased as well as having a positive signalapplied totits base, which prevents conduction. Diode-connectedtransistor XR2 preventsforward conduction through thebase to collectorjunctionof control transistor XR-l, when the emitter is negative.

A highlysatisfactory transistor power regulator is provided bya circuit.havingcomponent values as shown in the drawings. While specific values.and typesof com-. ponentsare given, these have been noted asv examplesonly, and are not intended to restrict the breadth and scope ofourpresent invention, 7

It is to be understood that the particular embodiment of our inventiondescribed above and shown in the drawings is merely illustrative of andnot restrictive of the broad invention, and that various changes indesign, structure and arrangement may be made without departing from thespirit and scope of the broader of the appended claims.

We claim:

1. A power regulator, comprising: a saturable core reactor having aprimary winding and a secondary winding; a first source of alternatingvoltage connected to energize one end of the primary winding; a controlsemiconductive device; an input network for applying an adjustablemagnitude control signal to said control semiconductive device, anoutput voltage being obtained therefrom according to the magnitude ofthe control signal and applied to the other end of the primary winding,the difference in magnitude between the alternating voltage of saidfirst source and the output voltage from said control semiconductivedevice appearing as a reset voltage across the primary winding forresetting said saturable core reactor during a conductive interval forsaid control semiconductive device; a power semicondurtive device fordriving a load when energized; a second source of alternating voltage,the secondary winding connecting said second source to said powersemiconductive device for energizing the same and driving the load whensaid saturable core reactor saturates, said saturable core reactorsaturating during a non-conductive interval for said controlsemiconductive device according to the magnitude of the reset voltagepreviously appl ed to the primary winding. whereby power delivered bysaid power semiconductive device to the load varies according to thereset of said saturable core reactor and the magnitude of the controlsignal.

2. A transistor power regulator. comprising: a saturable core reactorhaving a primary winding and a secondary winding; a control transistorhaving a base, emitter and collector, the emitter of said controltransistor being connected to one end of the primarv winding: a firstsource of alternating voltage connecting the co lector of s id controltransistor to the other end of the primary winding; an input network forapplving a control signal to the base of said control transistor forproducing an output voltage on the emitter of said control transistoraccording to the ma gnitude of the control signal, a reset voltage ofmagnitude equal to the difference in magnitude between the alternatingvoltage of said first source and the output voltage on the emitter ofsaid control transistor being developed across the primary winding forresetting said saturable core reactor during a conductive interval forsaid control transistor; a power transistor having a base, emitter andcollector, the base of said power trans stor being connected to one endof the secondary winding and the collector of said power transistorbeing connected to the other end of the secondary winding; a secondsource of alternating voltage having an output voltage in phase with theoutput voltage of said first source, said second source being connectedon one end to the collector of said power transistor and the other endof the secondary winding; and a load connecting the emitter of saidpower transistor to the other end of said second source. the alternatingvoltage of said second source being applied to the base of said powertransistor and energizing the same on saturation of said saturable corereactor occurring during a non-conductive interval for said controltransistor and according to the magnitude of the reset voltagepreviously developed across the primary winding, whereby power deliveredby said power transistor to said load varies according to the reset ofsaid saturable core reactor and the magnitude of the control signal.

3. The invention according to claim 2 wherein said load is connected inthe collector circuit of said power transistor and the emitter of saidpower transistor is connected directly to the other end of said secondsource of alternating voltage.

4. The invention according to claim 2 wherein said input networkincludes a resistance-capacitance coupling circuit, and the controlsignal is an alternating voltage which is in phase with the outputvoltages of said first and second sources.

5. The invention according to claim 2 wherein said control signal is adirect current control signal.

6. The invention according to claim 2 wherein said first and secondsources of alternating voltages include an autotransformer having outputvoltage taps for providing inphase alternating voltages of differentmagnitudes.

7. The invention according to claim 2 including, in addition,unidirectional conducting means connecting the base of said powertransistor to the one end of the secondary winding, for preventingleakage through said power transistor.

8. The invention according to claim 2 including, in addition,unidirectional conducting means for connecting the collector of saidpower transistor to the one end of said second source of alternatingvoltage, for preventing reversed conduction through said powertransistor when the emitter and collector of said power transistor arefunctionally interchangeable.

9. The invention according to claim 2 including, in addition,unidirectional conducting means for connecting the collector of saidcontrol transistor to said first source of alternating voltage, forpreventing reversed conduction through said control transistor when theemitter and collector of said control transistor are functionallyinterchangeable.

10. The invention according to claim 9 wherein said unidirectionalconducting means is a diode-connected transistor.

References Cited in the file of this patent UNITED STATES PATENTS2,569,345 Shea Sept. 25, 1951 2,760,088 Pittman et al. Aug. 21, 19562,808,990 Van Allen Oct. 8, 1957 2,809,303 Collins Oct. 8, 19572,809,343 Pittman Oct. 8, 1957 FOREIGN PATENTS 167,294 Australia Mar.21, 1956 OTHER REFERENCES Naval Research Laboratory Report 3869, On theControl of Magnetic Amplifiers, by R. A. Ramey, Oct. 24, 1951, pages1-9.

